miext/sync: Make struct _SyncObject::initialized fully ABI compatible

With a 32-bit build, putting the initialized field at the end of the
struct bumped the struct size from 20 bytes to 24, changing the layout
of other structs embedding struct _SyncObject. While this would be
acceptable on master, it caused crashes with 1.20.

Making the initialized field a char and putting it in the hole before
the beingDestroyed field restores the 32-bit ABI as well.

Fixes xorg/xserver#892

Reviewed-by: Aaron Plattner <aplattner@nvidia.com>
Reviewed-by: Alex Goins <agoins@nvidia.com>
3 jobs for miext-sync-fix-1.20-ABI-harder in 5 minutes and 40 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Docker Image
passed debian-testing #666431


  Build And Test
passed autotools-build-and-test #666432


passed meson-build-and-test #666433